The present invention relates generally to instruments for sampling fluids for analysis, and more particularly to a composite sampler which automatically collects fluid samples from high velocity sampling points without damaging particulate matter suspended therein or biasing the sample.
In the operation of a fish hatchery, it is often necessary to treat the hatchery water polluted by the build-up of waste matter of fish. Typically, grab samples are taken from hatchery water effluent every one-half hour around the clock in order to determine the amount of quality of solids present in the hatchery water. This procedure requires that a technician be on hand to perform the sampling.
In order to relieve the technician, automatic pump-driven composite samplers have been provided which periodically draw a sample of the hatchery water at a discharge tube into a collection container. The automatic composite samplers of the prior art, of which I am aware, have been somewhat unsatisfactory because the effluent at the discharge tube is actually drawn at low velocity through the pump on way to the sample chamber. The action of the pump destroys or alters the particulate matter. Also, the flow velocity of the water drawn with the sample chamber is less than that of the high velocity discharge, and a pressure head or "cone of rejection" is created at the chamber inlet tube. The effect of the pressure head is to bias the sample, i.e., draw a sample having less particulate matter than is representative of the discharge. Since proper analysis of the composite dictates that the suspended particulate matter be unadulterated and the samples be unbiased, the samples actually collected by prior art apparatus are inadequate.
Some prior art automatic composite samplers avoid damaging the suspended particulate matter in the sample by providing a sample chamber and locating the pump downstream of the chamber. The pump creates a negative pressure in the sample chamber, and draws the fluid up into the chamber for subsequent drainage into a collection container. The composite never reaches the pump so that the particulate matter is not altered or damaged. However, these systems are primarily adapted to be used in conjunction with static fluids. Accordingly, the velocity of fluids drawn by these apparatus is substantially lower than the velocity of effluent from a fish hatchery. The result is that the sample is biased.
Automatic composite samplers of which I am aware are disclosed in the U.S. Pat. Nos. to Carr 3,412,612 and Brooks, Sr. 3,589,197. While these systems function somewhat satisfactorily, each includes valves which must be operated by an external control means and is therefore relatively complex. For example, in Brooks, Sr., a flexible tube-type valve is controlled by an electrical solenoid which, along with the pump, is controlled by a timer. In Carr, a multi-valve sample chamber is controlled by a pair of electrical solenoids. The pair of solenoids is controlled by a timer; there is no pump and, in order to in-draw fluid, the sample chamber must be maintained beneath the surface of the fluid reservoir being sampled. The requirement of external control for the valves increases the cost and required maintenance of the samplers, and makes them unsuitable for low cost, high reliability applications. Neither Brooks, Sr. nor Carr discloses the use of a high velocity pump to eliminate biasing in the samples.